Concerns over the privacy of personal information on Facebook are nothing new--the latest involve the misappropriation of personal data by Facebook apps (an issue Facebook has committed itself to fixing). Even more troubling, federal agents are using Facebook to "friend" people as an investigatory tool, according to a FOIA investigation by the Electronic Frontier Foundation. Not too friendly.
Our electronic communications privacy laws are long out of date, and the ACLU is doing its best to fix that. But in the meantime, we all have to take responsibility for keeping our own information private: be careful about what you put in an email, think about who might view your Facebook page, and don't turn over private information (like a Social Security number) unless you understand what is going to happen to it and why. It is unfortunate that we should need to live our lives in such a guarded manner, but until the law improves, we do not have much choice.